Chemical sensitization of photographic emulsions



Patented Sept. 12, 1950 CHEMICAL SENSITIZATION OF PHOTO- GRAPHIC EMULSIONS Wesley G. Lowe and Jean E. Jones, Rochester, N. Y., assignors to Eastman Kodak Company, Rochester, N. Y., a corporation of New Jersey No Drawing. Application NovemberlS, 1948, Serial No. 60,817

11 Claims.

This invention relates to photographic emulsions and more particularly to chemical sensitizers therefor.

It is well known that silver halide emulsions may be chemically sensitized with a variety of materials so as to increase the speed and generally the gamma of the emulsions as opposed to optical sensitizing in which the optical range of sensitivity is increased. Depending upon the materials and methods employed, it is generally regarded that chemical sensitization results in either the formation of silver sulfide on the surface of the silver halide crystal or results in the formation of small amounts of silver from the reduction of silver halide, which effect may be in addition to the former effect usually known as sulfur sensitizing. The present invention is concerned primarily with chemical sensitization apparently of the latter type.

It has been proposed to use organic and inorganic sulfides in photographic emulsions to increase the sensitivity thereof. The compounds are generally regarded as imparting the abovementioned type of sulfur sensitizing resulting from the formation of silver sulfide nuclei on the silver halide grains. We have discovered a group of organic sulfur-containing compounds which have little or no activity as sulfur sensitizing agents but which appear to depend for their sensitizing effect upon enlargement of the silver sulfide nuclei by deposition of silver thereon through reduction of silver halide. Whatever the mechanism involved, the sensitizing effect is readily distinguishable from ordinary sulfur sensitizing and when employed in conjunction with sulful sensitizing can be separately evaluated.

One object of our invention is to provide photographic emulsions having increased sensitivities. Another object is to provide emulsions having sensitivities imparted by novel sulfur-containing compounds. A further object is to provide emulsions having sensitivities increased by means of both sulfur sensitizing and the novel sulfur-containing compounds. Another object is to provide sulfur-containing compounds which impart sensitivity to emulsions which effect is distinguishable from the sensitizing effect of ordinary sulfur sensitizers. Other objects of our invention will appear from the following description thereof:

The objects of our invention are accomplished in part by incorporating in silver halide emulsions, either bis-(daminoethyl) sulfide andits water-soluble salts obtained from nondesensitizing acids or bis-(y-diethyl aminopropyl) disulfide [(CzHs) 2NC31-IvS]2 at any stage in their preparation but preferably before digestion is complete. Generally in order to obtain the optimum sensitizing effect, we heat the emulsion after addition of the sensitizing agent. The sensitizing agents maybe used in conjunctionlwith other chemical Or optical sensitizers such as the well-known sulfur sensitizing compounds disclosed in Sheppards U. S. Patents 1,574,944, granted-March 2, 1926, and 1,623,499, granted April d, 1927, and may be employed before, after or simultaneously with sulfur sensitizing. Also, our novel sensitizers are useful in conjunction with-a variety of emulsions producing pronounced speed increases, particularly with fine-grained positive types of emulsions.

Our invention will now be illustrated by ref, erence to the following specific examples:

Example 1 A. 100 cc. sample of a bromo-iodide positive type.

of emulsion which had previously beenpeptized with a gelatin derivative and sulfur sensitized composition:

Water liters 1 p-Methylaminophenol sulfate grarns 0.3 Hydroquinone do 6.0 Sodium sulfite (dry) do 38.0 Sodium bisulfite do 1.2 Sodium carbonate (dry) do 19.0 Potassium bromide do 0.9- Citric acid do 017 The speed increase is apparent from consideration of the following table (sample D compared to samples A, B and C). sensitizing the emulsion in the manner described has thus produced a pronounced speed increase appreciably greater than that obtained from the individual sensitizing agents when used alone.

Example 2 A100. cc. sample of a bromo-iodide positive type of emulsion which had previously been peptized and sulfur sensitized with e. g. allylthin-- The 3 bper composition, the emulsion was found to have increased in speed as shown in the table following (sample F compared to E) In a similar manner, samples of the above emulsion were added to a solution of polyvinyl alcohol and after exposure and processing had the characteristics shown in the table followin (sample H compared to sample G). As in the previous example, the sensitizing agent will be seen to have exerted a synergistic sensitizing effeet in that the increase in sensitivity is greater than would be expected from the behavior of the individual sensitizing agents when used alone.

Sample Sensitizer Vehicle E i Gamma Fog None Gelatin... O. 58 1. 18 0.01

Sulfur type 2. 44 0.06

Sulfur and B".---- 3.05 0. O6

ployed in the above examples, one-fifth to five times as much sensitizer producing emulsions of useful sensitivity. Less heating is usually required when the larger amounts are employed and conversely when using the smaller quantities of sensitizer.

It will be noted in the above examples that the sensitizing of the emulsions with the novel sulfide compounds was effected at relatively low pH. This is not a limitation of our invention but more an advantage thereof since we are able to suppress sulfur sensitivity by lowering the pH of the emulsion and since the novel sulfide sensitizers are so active, further sensitization takes place even substantially below the neutral point when they are added to the emulsion.

The novel sensitizers may, in general, be employed in hydrophilic colloid emulsion vehicles; for example, gelatin, polyvinyl alcohol, partially hydrolyzed cellulose esters, such as cellulose acetate and co-polymers of polyvinyl alcohol. The

ratio of colloid, to silver halide present durin the digestion is not critical in this type of sensitizing since the digestion conditions can be readily adjusted as is well known in the art of sulfur sensitizing. The sensitizers are suitable for the well known types of silver chloride, silver bromide and silver iodide emulsions and emulsions containing mixtures of these halides, containing the usual emulsion addenda such as antifoggants, spreading agents, coupler compounds, etc. Such emulsions are suitable to use in forming single as well as multi-layer film useful in color photography which customarily include on a support two or more emulsion layers sensitized to different regions of the visible spectrum and may or may not contain coupler compounds. According to our invention such color films carry at least one emulsion layer containing a sulfide sensitizing agent of our invention.

Our invention having been described, we would have it understood that the preceding description is by way of example only and that our in vention is to be taken as limited only by the scope of the appended claims.

What we claim is:

1. A light-sensitive photographic emulsion comprising silver halide and a sensitizing agent selected from the group consisting of bis-(p-aminoethybsulfide and Water soluble salts thereof, and bis-(Y-diethyl aminopropyl) disulfide.

2. A light-sensitive photographic emulsion comprising silver halide and bis-(,S-aminoethyl) sulfide as a sensitizing agent.

3. A light-sensitive photographic emulsion comprising sulfur sensitized silver halide and bis-(fi-aminoethyl) sulfide as an additional sensitizing agent.

4. A light-sensitive photographic emulsion comprising silver halide and bis-('y-diethylaminopropyl) disulfide as a sensitizing agent.

5. A light-sensitive photographic emulsion comprising sulfur sensitized silver halide and bis-(Y-diethylamino propyl) disulfide as an additional sensitizing agent.

6. The method of increasing the speed of a photographic silver halide emulsion which comprises imparting sulfur sensitivity to said emulsion, adjusting th pH of said emulsion to below neutrality and effecting a further increase in sensitivity by digestion of said emulsion in the presence of a sensitizing agent selected from the group consisting of bis-(B-aminoethyl) sulfide and water soluble salts thereof, and bis-("y-diethyl aminopropyl) disulfide.

7. The method of increasing the speed of a photographic silver halide emulsion which comprises imparting sulfur sensitivity to said emulsion, adjusting the pH of said emulsion to below neutralit and effecting a further increase in sensitivity by digestion of said emulsion in the presence of bis-(B-aminoethyl) sulfide.

8. The method of increasing the speed of a photographic silver halide emulsion which comprises imparting sulfur sensitivity to said emulsion, adjusting the pH of said emulsion to below neutrality and effecting a further increase in sensitivit by digestion of said emulsion in the presence of bis-(Y-diethylaminopropyl) disulfide.

9. The method of increasing the speed of a photographic silver halide emulsion which comprises digesting said emulsion in the presence of a, sulfur sensitizing agent and a sensitizing agent selected from the group consisting of bis-(B-aminoethyl) sulfide and water soluble salts thereof, and bis-(v-diethyl aminopropyl) disulfide.

10. The method of increasing the speed of a photographic silver halide emulsion which comprises digesting said emulsion in the presenc of a sulfur sensitizing agent and bis(,8-aminoethyl) sulfide.

11. The method of increasing the speed of a photographic silver halide emulsion which comprises digesting said emulsion in the presence of a sulfur sensitizing agent and bis (Y-diethylaminopropyl) disulfide.

WESLEY G. LOWE. JEAN E. JONES.

REFERENCES CITED FOREIGN PATENTS Country Date Great Britain Nov, 21. 1938 N umber 

1. A LIGHT-SENSTIVE PHOTOGRAPHIC EMULSION COMPRISING SILVER HALIDE AND A SENSITIZING AGENT SELETED FROM THE GROUP CONSISTING OF BIS- (B-AMINOETHYL) SULFIDE AND WATER SOLUBLE SALTS THEREOF, AND BIS-(Y-DIETHYL AMINOPROPY) DISULFIDE. 